Batteries have been widely used as power sources of various electronic devices. Examples of battery types include primary batteries typified by dry batteries, and secondary batteries that can be repeatedly charged and discharged. While examples of the shape of each of these batteries include various shapes, such as a cylindrical shape, a prismatic shape, and a sheet-like shape, columnar batteries are most common.
In recent years, there have been increasing demands for, for example, reusable nickel-hydrogen secondary batteries, reusable nickel-cadmium secondary batteries, and reusable lithium ion secondary batteries to save resources and energy. Among them, lithium ion secondary batteries are characterized by lightness in weight, high electromotive force, and high energy density. Thus, there are growing demands for the lithium ion secondary batteries as power sources for driving various kinds of mobile electronic devices and portable communication devices such as mobile phones, digital cameras, video cameras, and laptop personal computers. While lithium ion secondary batteries have various shapes, a large amount of standardized cylindrical batteries are produced, and examples of the standardized cylindrical batteries include 18650-sized batteries, 17670-sized batteries, 18500-sized batteries, 17500-sized batteries, 16340-sized batteries, and 14500-sized batteries.
Since lithium ion secondary batteries have high energy density, shorting causes the generation of a large amount of heat. Thus, processes for transporting lithium ion secondary batteries are strictly controlled, and in order to prevent an adjacent pair of batteries from being in contact with each other and thus being shorted to each other, the batteries have been packaged so as to be reliably spaced apart from one another, or so as to be each enclosed with insulating material (e.g., PATENT DOCUMENTS 1 and 2).